A conventional transfer pump 100 for pumping a viscous material to relatively high pressures is shown in FIG. 1. An example of a pump generally of the type shown in FIG. 1 is the OP232 Series Polyurethane pump marketed by International Pump Manufacturing Inc. The pump 100 has a motor 102, for example, an air motor with an air inlet valve 101. The motor 102 is configured to drive a pump drive shaft 103 in a reciprocating motion. A plurality of standoffs 104 attach the motor 102 to a pump body 106. The pump body 106 includes three small-diameter tubes 110 that are fluidly connected at an upper end with a pump outlet manifold 108, and are fluidly connected at the opposite end to a suction or pressure cylinder 112. The bottom end of the pressure cylinder 112 has a ball-type foot valve 114. During use the foot valve 114 end of the pump 100 is typically inserted directly into a large container or reservoir of material to be pumped. The material is then drawn through the foot valve 114 and pressurized as discussed below.
FIG. 2 is a schematic illustration of the pump 100, illustrating the operation of the pump 100. The pump 100 is a double-acting pump, i.e., a pumping or pressurizing action is achieved on both the down-stroke and the up-stroke of the pump shaft 103. The motor indicated by the arrow 102 drives the pump shaft 103 in reciprocating motion. The pump shaft 103 extends downwardly through a center channel in the outlet manifold 108, between the small tubes 110 and into the pressure cylinder 112. The base 116 of the pump body 106 is attached to the pressure cylinder 112, such that the small tubes 110 are fluidly connected to the pressure cylinder 112.
An inner cylinder 118 extends downwardly from the base 116 coaxially within the pressure cylinder 112. Therefore an annular flow region 117 is formed between the inner cylinder 118 and the pressure cylinder 112. A smaller cylindrical volume is defined by the interior of the inner cylinder 118. A large piston 120 is attached to the distal end of the pump shaft 103 and slidably engages the pressure cylinder 112. The large piston 120 includes an inner check valve 122 that closes from fluid pressure when the large piston 120 is moving up, and opens when the large piston 120 is moving down. The foot valve 114 opens when the large piston 120 is moving up, and closes when the large piston 120 is moving down. A small piston 124 is attached at an intermediate location to the pump shaft 103, and slidably reciprocates within the inner cylinder 118.
The operation of the pump 100 can now be understood. During the up-stroke, the inner check valve 122 closes, and the foot valve 114 opens, such that material is drawn into the pressure cylinder 112 from the reservoir 90 (arrow 91). The material above the large piston 120 is pressurized by the upwardly moving large piston 120. A portion of the fluid in the pressure cylinder 112 enters the inner cylinder 118 (arrows 93), and a portion flows through the annular region 117 and into the small tubes 110 (arrows 94).
During the down-stroke of the pump shaft 103, the foot valve 114 closes and the inner check valve 122 opens such that the material below the large piston 120 flows through the inner check valve 122 (arrow 92). The small piston 124 also moves downwardly, forcing material from the inner cylinder 118 (arrows 93) into the region below, again pressurizing the pressure cylinder 112. Material is therefore flows through the annular region 117 and into the small tubes 110. The pressurized material forced into the small tubes 110 is thereby ejected from the outlet manifold 108 (arrow 95), typically to a spray gun or other dispersal tool (not shown).
The transfer pump 100 of the type disclosed has performed well in the art for suitable applications. However, there are some disadvantages to the pump 100. For example, forcing very viscous material through multiple small tubes 110 requires a lot of work, and the small tubes may be difficult to clean and are prone to clogging. Also, during shipping, maintenance, or the like, the small tubes 110 may become bent or otherwise damaged. Also, due to leakage through the base 116 of the pump body at the pump shaft 103 seal, in the past it has not been practical to mount the pump 100 away from the material reservoir (e.g., with a wall mount), using a flexible conduit to fluidly connect the foot check valve 114 with the material.